With remarkable advances in computer and semiconductor technologies, electronic devices, such as media players, gaming devices, cellular phones, navigational devices, etc., have become more popular and affordable for most users. In these electronic devices, there is a prevailing trend for three-dimensional display to provide the user with a better visual enjoyment and understanding than traditional two-dimensional display.
In some navigation devices and systems with so-called “three-dimensional” display, there is typically a two-dimensional overlay showing turns or maneuvers in a static, but detailed image. Such an approach requires the user to translate this two-dimensional view into the three-dimensional reality which the users see the surroundings and a guidance route directly or through a vehicle windshield. This may cause confusion in routing situations where two or more turns are closely spaced together with roads which are not part of the guidance route.
For example, U.S. Pat. No. 6,285,317 issued to Ong discloses a navigation system for a ground vehicle which incorporates a three-dimensional display updated with information from a wireless service provider. However, the three-dimensional display disclosed by Ong is directed simply to a real environmental scene overlaid with a three-dimensional turn icon.
Furthermore, U.S. Pat. No. 7,039,521 issued to Hortner et al. discloses a method and device for displaying driving instructions. More particularly, when calculating the perspective view from the viewpoint of the user, the inclination of the vehicle about its longitudinal and lateral axes relative to the road surface is taken into account, as is the incline of the road or the three-dimensionality of the terrain. However, like Ong, Hortner merely discloses three-dimensional driving instructions overlaying on real-time images taken by a camera.
Conventionally, displaying road and polygon (map) information over three-dimensional terrain poses difficult challenges. For example, the roads may “dig into” or “fly above” the terrain proximate to them. In other words, if a long road segment crosses a hill or valley, it is very likely that the road no longer appears connected to the ground of the terrain. The road may be under or over the terrain surface, which may cause visual discomfort for the user. One solution is proposed to dynamically generate roads which conform to the terrain below, over different levels of detail (LOD). However, showing high LOD terrains and road images requires a large amount of memory and a high processing capability.
Therefore, there remains a need for a display method and apparatus to provide three-dimensional route guidance in a three-dimensional rendering environment with dynamic control of level of details, viewing angles, and heights of objects without high computation requirements.